Algae are simple plant-like living organisms. They are unicellular or multicellular living organisms. Algae are found in nature and are divided into different classes and are found in variety of colours and forms. Owing to their high nutritional value, declining food sources, constantly rising population and decreasing agriculture land, algae are considered as potential food for future. Besides nutritional components, algae particularly microalgae are also a major source of valuable additives, other compounds and pigments with therapeutic, chemo-preventive nature and industrial applications.
Carotenoids are class of such pigments having an array of applications which include health food products, cosmetics, feed additives for poultry, livestock, fishes, crustaceans, therapeutic and chemo-preventive supplements in pharmaceuticals and also as colouring agent in various industries. The nutraceutical boom has also added to the demand of mixed carotenoids mainly on the claim of their proven antioxidant and therapeutic properties. Such and other recently discovered health benefits have furthered the market potential of carotenoids. The growing worldwide market value of carotenoids is projected to reach over US$1,000 million in near future. Consumers' demand for natural products favours development of carotenoids from biological sources rather than from synthetic routes due to the problem of toxicity.
Many studies have revealed that natural mixed carotenoids have better synergistic effect and provide more antioxidant protection than individual carotenoid components. This has led to increased interest to obtain natural mixed carotenoids rather than individual carotenoid fractions. Natural mixed carotenoids can be obtained from the biological sources including plant material or microalgae. However, productivity and percentage of carotenoid synthesis in plants is relatively low, as a result, the carotenoids produced from plants are more expensive. Several microalgae including blue-green algae are found to contain carotenoids and there has been increased interest to exploit them to produce natural mixed carotenoids.
Spirulina is a primitive form of prokaryotic blue-green microalgae belonging to division (phylum) cyanobacteria. Spirulina species are photosynthetic, filamentous, rod to spiral-shaped. The most important species are Spirulina maxima, Spirulina fusiformis, Spirulina pacifica, Spirulina platensis and many more. Spirulina is a valuable source for natural bioactive and nutritional constituents possessing diverse biological activities and nutritional significance. The recent studies also have indicated the antioxidant and immunostimulatory activity of Spirulina is attributed to its mixed carotenoids and polysaccharide fractions.
The chemical composition of Spirulina includes proteins 55000-72000 mg per 100 gm, carbohydrates 15000-25000 mg per 100 gm, fats (lipids) 6000-8000 mg per 100 gm, along with vitamins 350-650 mg per 100 gm, minerals 5000-7000 mg per 100 gm, pigments like natural mixed carotenoids 370 mg per 100 gm, chlorophyll-a 1000 mg per 100 gm and phycocyanin 14000 mg per 100 gm. The natural mixed carotenoid fraction of the Spirulina is reported to consist of beta-carotenes, zeaxanthene, echinenone, beta-cryptoxanthene, hydroxyechinenone, and other carotenoids. There has been an increasing demand world over for growing Spirulina for its end application in food and feed supplements, nutraceuticals and cosmetics. However, its intense blue-green colour and other organoleptic characteristics such as taste and flavour are also not so pleasant, limits its major commercial applications.
There have been many culture protocols, which have been proposed to produce conventionally available Spirulina. 
CN121883 relates to the growth and propagation of blue-green algae. It discloses a method for regulating and controlling carbon source and pH value in cultivating Spirulina. NaHCO3 or carbon dioxide is added to the culture medium for precise control of pH so as to promote the growth and propagation of blue-green algae.
CN1254012 relates to cultivating edible fresh Spirulina, in inorganic compounds containing NaHCO3 with a pH of 8-11 and water temperature of 25-40 deg C.
RO117388 discloses a mutant of Spirulina platensis grown in continuous flow cultivation with medium possessing NaHCO3, NaNO3 and other inorganic nutrients.
JP1037281 reflects a culture method for marine blue-green algae with steps of adding condensed phosphate at specific dosages to the culture solution, dissociating ample iron ion, and maintaining a dissolution state to promote their growths. As described above, Na2CO3, NaHCO3, NaH2PO4 and other inorganic salts are added as nutrients. pH adjuster or buffer is added to obtain the desired pH level suitable for algae growth.
AU2004322412 reflects process for biomass generation of Spirulina at pH of 6.5 and 8.0 with bicarbonate of sodium in the range of 1.2 to 3.0% w/v, nitrogen content in the range 0.1 to 0.3% w/v, phosphorus in the range 0.1 to 0.3% w/v and potassium in the range 0.1 to 0.3% w/v in a sea water based medium.
The patent documents as mentioned above only reveal nutrient inputs and steps for obtaining higher biomass of Spirulina. 
There have been even attempts to propose protocols to selectively increase some of the nutritional components such as iron, selenium, geranium or others.
CN1144844 relates to manufacture of iron rich Spirulina with ferrous methionine usage.
CN1092104 discloses cultivation of Spirulina in geranium dioxide and sodium selenite to produce Spirulina containing geranium and selenium.
However, so far there have not been any successful attempts to grow Spirulina or other microalgae including blue-green algae with increased natural mixed carotenoids contents with significantly high amounts. Besides, there have been no significant efforts focused on producing Spirulina with visually agreeable appearance and improved organoleptic characteristics.
Thus, there is an unmet demand to cultivate microalgae including Spirulina and other blue-green algae with increased contents of natural mixed carotenoids, with visually agreeable appearance and organoleptic characteristics.